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99033461e6
linux/tools/objtool/check.c
Josh Poimboeuf 99033461e6 objtool: Support asm jump tables 
Objtool detection of asm jump tables would normally just work, except
for the fact that asm retpolines use alternatives.  Objtool thinks the
alternative code path (a jump to the retpoline) is a sibling call.

Don't treat alternative indirect branches as sibling calls when the
original instruction has a jump table.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Link: https://lore.kernel.org/r/460cf4dc675d64e1124146562cabd2c05aa322e8.1614182415.git.jpoimboe@redhat.com
2021-04-19 12:36:32 -05:00

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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
*/
#include <string.h>
#include <stdlib.h>
#include <arch/elf.h>
#include <objtool/builtin.h>
#include <objtool/cfi.h>
#include <objtool/arch.h>
#include <objtool/check.h>
#include <objtool/special.h>
#include <objtool/warn.h>
#include <objtool/endianness.h>
#include <linux/objtool.h>
#include <linux/hashtable.h>
#include <linux/kernel.h>
#include <linux/static_call_types.h>
struct alternative {
struct list_head list;
struct instruction *insn;
bool skip_orig;
};
struct cfi_init_state initial_func_cfi;
struct instruction *find_insn(struct objtool_file *file,
struct section *sec, unsigned long offset)
{
struct instruction *insn;
hash_for_each_possible(file->insn_hash, insn, hash, sec_offset_hash(sec, offset)) {
if (insn->sec == sec && insn->offset == offset)
return insn;
}
return NULL;
}
static struct instruction *next_insn_same_sec(struct objtool_file *file,
struct instruction *insn)
{
struct instruction *next = list_next_entry(insn, list);
if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
return NULL;
return next;
}
static struct instruction *next_insn_same_func(struct objtool_file *file,
struct instruction *insn)
{
struct instruction *next = list_next_entry(insn, list);
struct symbol *func = insn->func;
if (!func)
return NULL;
if (&next->list != &file->insn_list && next->func == func)
return next;
/* Check if we're already in the subfunction: */
if (func == func->cfunc)
return NULL;
/* Move to the subfunction: */
return find_insn(file, func->cfunc->sec, func->cfunc->offset);
}
static struct instruction *prev_insn_same_sym(struct objtool_file *file,
struct instruction *insn)
{
struct instruction *prev = list_prev_entry(insn, list);
if (&prev->list != &file->insn_list && prev->func == insn->func)
return prev;
return NULL;
}
#define func_for_each_insn(file, func, insn) \
for (insn = find_insn(file, func->sec, func->offset); \
insn; \
insn = next_insn_same_func(file, insn))
#define sym_for_each_insn(file, sym, insn) \
for (insn = find_insn(file, sym->sec, sym->offset); \
insn && &insn->list != &file->insn_list && \
insn->sec == sym->sec && \
insn->offset < sym->offset + sym->len; \
insn = list_next_entry(insn, list))
#define sym_for_each_insn_continue_reverse(file, sym, insn) \
for (insn = list_prev_entry(insn, list); \
&insn->list != &file->insn_list && \
insn->sec == sym->sec && insn->offset >= sym->offset; \
insn = list_prev_entry(insn, list))
#define sec_for_each_insn_from(file, insn) \
for (; insn; insn = next_insn_same_sec(file, insn))
#define sec_for_each_insn_continue(file, insn) \
for (insn = next_insn_same_sec(file, insn); insn; \
insn = next_insn_same_sec(file, insn))
static bool is_jump_table_jump(struct instruction *insn)
{
struct alt_group *alt_group = insn->alt_group;
if (insn->jump_table)
return true;
/* Retpoline alternative for a jump table? */
return alt_group && alt_group->orig_group &&
alt_group->orig_group->first_insn->jump_table;
}
static bool is_sibling_call(struct instruction *insn)
{
/*
* Assume only ELF functions can make sibling calls. This ensures
* sibling call detection consistency between vmlinux.o and individual
* objects.
*/
if (!insn->func)
return false;
/* An indirect jump is either a sibling call or a jump to a table. */
if (insn->type == INSN_JUMP_DYNAMIC)
return !is_jump_table_jump(insn);
/* add_jump_destinations() sets insn->call_dest for sibling calls. */
return (is_static_jump(insn) && insn->call_dest);
}
/*
* This checks to see if the given function is a "noreturn" function.
*
* For global functions which are outside the scope of this object file, we
* have to keep a manual list of them.
*
* For local functions, we have to detect them manually by simply looking for
* the lack of a return instruction.
*/
static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
int recursion)
{
int i;
struct instruction *insn;
bool empty = true;
/*
* Unfortunately these have to be hard coded because the noreturn
* attribute isn't provided in ELF data.
*/
static const char * const global_noreturns[] = {
"__stack_chk_fail",
"panic",
"do_exit",
"do_task_dead",
"__module_put_and_exit",
"complete_and_exit",
"__reiserfs_panic",
"lbug_with_loc",
"fortify_panic",
"usercopy_abort",
"machine_real_restart",
"rewind_stack_do_exit",
"kunit_try_catch_throw",
"xen_start_kernel",
};
if (!func)
return false;
if (func->bind == STB_WEAK)
return false;
if (func->bind == STB_GLOBAL)
for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
if (!strcmp(func->name, global_noreturns[i]))
return true;
if (!func->len)
return false;
insn = find_insn(file, func->sec, func->offset);
if (!insn->func)
return false;
func_for_each_insn(file, func, insn) {
empty = false;
if (insn->type == INSN_RETURN)
return false;
}
if (empty)
return false;
/*
* A function can have a sibling call instead of a return. In that
* case, the function's dead-end status depends on whether the target
* of the sibling call returns.
*/
func_for_each_insn(file, func, insn) {
if (is_sibling_call(insn)) {
struct instruction *dest = insn->jump_dest;
if (!dest)
/* sibling call to another file */
return false;
/* local sibling call */
if (recursion == 5) {
/*
* Infinite recursion: two functions have
* sibling calls to each other. This is a very
* rare case. It means they aren't dead ends.
*/
return false;
}
return __dead_end_function(file, dest->func, recursion+1);
}
}
return true;
}
static bool dead_end_function(struct objtool_file *file, struct symbol *func)
{
return __dead_end_function(file, func, 0);
}
static void init_cfi_state(struct cfi_state *cfi)
{
int i;
for (i = 0; i < CFI_NUM_REGS; i++) {
cfi->regs[i].base = CFI_UNDEFINED;
cfi->vals[i].base = CFI_UNDEFINED;
}
cfi->cfa.base = CFI_UNDEFINED;
cfi->drap_reg = CFI_UNDEFINED;
cfi->drap_offset = -1;
}
static void init_insn_state(struct insn_state *state, struct section *sec)
{
memset(state, 0, sizeof(*state));
init_cfi_state(&state->cfi);
/*
* We need the full vmlinux for noinstr validation, otherwise we can
* not correctly determine insn->call_dest->sec (external symbols do
* not have a section).
*/
if (vmlinux && noinstr && sec)
state->noinstr = sec->noinstr;
}
/*
* Call the arch-specific instruction decoder for all the instructions and add
* them to the global instruction list.
*/
static int decode_instructions(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;
unsigned long offset;
struct instruction *insn;
unsigned long nr_insns = 0;
int ret;
for_each_sec(file, sec) {
if (!(sec->sh.sh_flags & SHF_EXECINSTR))
continue;
if (strcmp(sec->name, ".altinstr_replacement") &&
strcmp(sec->name, ".altinstr_aux") &&
strncmp(sec->name, ".discard.", 9))
sec->text = true;
if (!strcmp(sec->name, ".noinstr.text") ||
!strcmp(sec->name, ".entry.text"))
sec->noinstr = true;
for (offset = 0; offset < sec->len; offset += insn->len) {
insn = malloc(sizeof(*insn));
if (!insn) {
WARN("malloc failed");
return -1;
}
memset(insn, 0, sizeof(*insn));
INIT_LIST_HEAD(&insn->alts);
INIT_LIST_HEAD(&insn->stack_ops);
init_cfi_state(&insn->cfi);
insn->sec = sec;
insn->offset = offset;
ret = arch_decode_instruction(file->elf, sec, offset,
sec->len - offset,
&insn->len, &insn->type,
&insn->immediate,
&insn->stack_ops);
if (ret)
goto err;
hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
list_add_tail(&insn->list, &file->insn_list);
nr_insns++;
}
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC || func->alias != func)
continue;
if (!find_insn(file, sec, func->offset)) {
WARN("%s(): can't find starting instruction",
func->name);
return -1;
}
sym_for_each_insn(file, func, insn)
insn->func = func;
}
}
if (stats)
printf("nr_insns: %lu\n", nr_insns);
return 0;
err:
free(insn);
return ret;
}
static struct instruction *find_last_insn(struct objtool_file *file,
struct section *sec)
{
struct instruction *insn = NULL;
unsigned int offset;
unsigned int end = (sec->len > 10) ? sec->len - 10 : 0;
for (offset = sec->len - 1; offset >= end && !insn; offset--)
insn = find_insn(file, sec, offset);
return insn;
}
/*
* Mark "ud2" instructions and manually annotated dead ends.
*/
static int add_dead_ends(struct objtool_file *file)
{
struct section *sec;
struct reloc *reloc;
struct instruction *insn;
/*
* By default, "ud2" is a dead end unless otherwise annotated, because
* GCC 7 inserts it for certain divide-by-zero cases.
*/
for_each_insn(file, insn)
if (insn->type == INSN_BUG)
insn->dead_end = true;
/*
* Check for manually annotated dead ends.
*/
sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
if (!sec)
goto reachable;
list_for_each_entry(reloc, &sec->reloc_list, list) {
if (reloc->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s", sec->name);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (insn)
insn = list_prev_entry(insn, list);
else if (reloc->addend == reloc->sym->sec->len) {
insn = find_last_insn(file, reloc->sym->sec);
if (!insn) {
WARN("can't find unreachable insn at %s+0x%x",
reloc->sym->sec->name, reloc->addend);
return -1;
}
} else {
WARN("can't find unreachable insn at %s+0x%x",
reloc->sym->sec->name, reloc->addend);
return -1;
}
insn->dead_end = true;
}
reachable:
/*
* These manually annotated reachable checks are needed for GCC 4.4,
* where the Linux unreachable() macro isn't supported. In that case
* GCC doesn't know the "ud2" is fatal, so it generates code as if it's
* not a dead end.
*/
sec = find_section_by_name(file->elf, ".rela.discard.reachable");
if (!sec)
return 0;
list_for_each_entry(reloc, &sec->reloc_list, list) {
if (reloc->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s", sec->name);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (insn)
insn = list_prev_entry(insn, list);
else if (reloc->addend == reloc->sym->sec->len) {
insn = find_last_insn(file, reloc->sym->sec);
if (!insn) {
WARN("can't find reachable insn at %s+0x%x",
reloc->sym->sec->name, reloc->addend);
return -1;
}
} else {
WARN("can't find reachable insn at %s+0x%x",
reloc->sym->sec->name, reloc->addend);
return -1;
}
insn->dead_end = false;
}
return 0;
}
static int create_static_call_sections(struct objtool_file *file)
{
struct section *sec, *reloc_sec;
struct reloc *reloc;
struct static_call_site *site;
struct instruction *insn;
struct symbol *key_sym;
char *key_name, *tmp;
int idx;
sec = find_section_by_name(file->elf, ".static_call_sites");
if (sec) {
INIT_LIST_HEAD(&file->static_call_list);
WARN("file already has .static_call_sites section, skipping");
return 0;
}
if (list_empty(&file->static_call_list))
return 0;
idx = 0;
list_for_each_entry(insn, &file->static_call_list, static_call_node)
idx++;
sec = elf_create_section(file->elf, ".static_call_sites", SHF_WRITE,
sizeof(struct static_call_site), idx);
if (!sec)
return -1;
reloc_sec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
if (!reloc_sec)
return -1;
idx = 0;
list_for_each_entry(insn, &file->static_call_list, static_call_node) {
site = (struct static_call_site *)sec->data->d_buf + idx;
memset(site, 0, sizeof(struct static_call_site));
/* populate reloc for 'addr' */
reloc = malloc(sizeof(*reloc));
if (!reloc) {
perror("malloc");
return -1;
}
memset(reloc, 0, sizeof(*reloc));
insn_to_reloc_sym_addend(insn->sec, insn->offset, reloc);
if (!reloc->sym) {
WARN_FUNC("static call tramp: missing containing symbol",
insn->sec, insn->offset);
return -1;
}
reloc->type = R_X86_64_PC32;
reloc->offset = idx * sizeof(struct static_call_site);
reloc->sec = reloc_sec;
elf_add_reloc(file->elf, reloc);
/* find key symbol */
key_name = strdup(insn->call_dest->name);
if (!key_name) {
perror("strdup");
return -1;
}
if (strncmp(key_name, STATIC_CALL_TRAMP_PREFIX_STR,
STATIC_CALL_TRAMP_PREFIX_LEN)) {
WARN("static_call: trampoline name malformed: %s", key_name);
return -1;
}
tmp = key_name + STATIC_CALL_TRAMP_PREFIX_LEN - STATIC_CALL_KEY_PREFIX_LEN;
memcpy(tmp, STATIC_CALL_KEY_PREFIX_STR, STATIC_CALL_KEY_PREFIX_LEN);
key_sym = find_symbol_by_name(file->elf, tmp);
if (!key_sym) {
if (!module) {
WARN("static_call: can't find static_call_key symbol: %s", tmp);
return -1;
}
/*
* For modules(), the key might not be exported, which
* means the module can make static calls but isn't
* allowed to change them.
*
* In that case we temporarily set the key to be the
* trampoline address. This is fixed up in
* static_call_add_module().
*/
key_sym = insn->call_dest;
}
free(key_name);
/* populate reloc for 'key' */
reloc = malloc(sizeof(*reloc));
if (!reloc) {
perror("malloc");
return -1;
}
memset(reloc, 0, sizeof(*reloc));
reloc->sym = key_sym;
reloc->addend = is_sibling_call(insn) ? STATIC_CALL_SITE_TAIL : 0;
reloc->type = R_X86_64_PC32;
reloc->offset = idx * sizeof(struct static_call_site) + 4;
reloc->sec = reloc_sec;
elf_add_reloc(file->elf, reloc);
idx++;
}
if (elf_rebuild_reloc_section(file->elf, reloc_sec))
return -1;
return 0;
}
static int create_mcount_loc_sections(struct objtool_file *file)
{
struct section *sec, *reloc_sec;
struct reloc *reloc;
unsigned long *loc;
struct instruction *insn;
int idx;
sec = find_section_by_name(file->elf, "__mcount_loc");
if (sec) {
INIT_LIST_HEAD(&file->mcount_loc_list);
WARN("file already has __mcount_loc section, skipping");
return 0;
}
if (list_empty(&file->mcount_loc_list))
return 0;
idx = 0;
list_for_each_entry(insn, &file->mcount_loc_list, mcount_loc_node)
idx++;
sec = elf_create_section(file->elf, "__mcount_loc", 0, sizeof(unsigned long), idx);
if (!sec)
return -1;
reloc_sec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
if (!reloc_sec)
return -1;
idx = 0;
list_for_each_entry(insn, &file->mcount_loc_list, mcount_loc_node) {
loc = (unsigned long *)sec->data->d_buf + idx;
memset(loc, 0, sizeof(unsigned long));
reloc = malloc(sizeof(*reloc));
if (!reloc) {
perror("malloc");
return -1;
}
memset(reloc, 0, sizeof(*reloc));
if (insn->sec->sym) {
reloc->sym = insn->sec->sym;
reloc->addend = insn->offset;
} else {
reloc->sym = find_symbol_containing(insn->sec, insn->offset);
if (!reloc->sym) {
WARN("missing symbol for insn at offset 0x%lx\n",
insn->offset);
return -1;
}
reloc->addend = insn->offset - reloc->sym->offset;
}
reloc->type = R_X86_64_64;
reloc->offset = idx * sizeof(unsigned long);
reloc->sec = reloc_sec;
elf_add_reloc(file->elf, reloc);
idx++;
}
if (elf_rebuild_reloc_section(file->elf, reloc_sec))
return -1;
return 0;
}
/*
* Warnings shouldn't be reported for ignored functions.
*/
static void add_ignores(struct objtool_file *file)
{
struct instruction *insn;
struct section *sec;
struct symbol *func;
struct reloc *reloc;
sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
if (!sec)
return;
list_for_each_entry(reloc, &sec->reloc_list, list) {
switch (reloc->sym->type) {
case STT_FUNC:
func = reloc->sym;
break;
case STT_SECTION:
func = find_func_by_offset(reloc->sym->sec, reloc->addend);
if (!func)
continue;
break;
default:
WARN("unexpected relocation symbol type in %s: %d", sec->name, reloc->sym->type);
continue;
}
func_for_each_insn(file, func, insn)
insn->ignore = true;
}
}
/*
* This is a whitelist of functions that is allowed to be called with AC set.
* The list is meant to be minimal and only contains compiler instrumentation
* ABI and a few functions used to implement *_{to,from}_user() functions.
*
* These functions must not directly change AC, but may PUSHF/POPF.
*/
static const char *uaccess_safe_builtin[] = {
/* KASAN */
"kasan_report",
"kasan_check_range",
/* KASAN out-of-line */
"__asan_loadN_noabort",
"__asan_load1_noabort",
"__asan_load2_noabort",
"__asan_load4_noabort",
"__asan_load8_noabort",
"__asan_load16_noabort",
"__asan_storeN_noabort",
"__asan_store1_noabort",
"__asan_store2_noabort",
"__asan_store4_noabort",
"__asan_store8_noabort",
"__asan_store16_noabort",
"__kasan_check_read",
"__kasan_check_write",
/* KASAN in-line */
"__asan_report_load_n_noabort",
"__asan_report_load1_noabort",
"__asan_report_load2_noabort",
"__asan_report_load4_noabort",
"__asan_report_load8_noabort",
"__asan_report_load16_noabort",
"__asan_report_store_n_noabort",
"__asan_report_store1_noabort",
"__asan_report_store2_noabort",
"__asan_report_store4_noabort",
"__asan_report_store8_noabort",
"__asan_report_store16_noabort",
/* KCSAN */
"__kcsan_check_access",
"kcsan_found_watchpoint",
"kcsan_setup_watchpoint",
"kcsan_check_scoped_accesses",
"kcsan_disable_current",
"kcsan_enable_current_nowarn",
/* KCSAN/TSAN */
"__tsan_func_entry",
"__tsan_func_exit",
"__tsan_read_range",
"__tsan_write_range",
"__tsan_read1",
"__tsan_read2",
"__tsan_read4",
"__tsan_read8",
"__tsan_read16",
"__tsan_write1",
"__tsan_write2",
"__tsan_write4",
"__tsan_write8",
"__tsan_write16",
"__tsan_read_write1",
"__tsan_read_write2",
"__tsan_read_write4",
"__tsan_read_write8",
"__tsan_read_write16",
"__tsan_atomic8_load",
"__tsan_atomic16_load",
"__tsan_atomic32_load",
"__tsan_atomic64_load",
"__tsan_atomic8_store",
"__tsan_atomic16_store",
"__tsan_atomic32_store",
"__tsan_atomic64_store",
"__tsan_atomic8_exchange",
"__tsan_atomic16_exchange",
"__tsan_atomic32_exchange",
"__tsan_atomic64_exchange",
"__tsan_atomic8_fetch_add",
"__tsan_atomic16_fetch_add",
"__tsan_atomic32_fetch_add",
"__tsan_atomic64_fetch_add",
"__tsan_atomic8_fetch_sub",
"__tsan_atomic16_fetch_sub",
"__tsan_atomic32_fetch_sub",
"__tsan_atomic64_fetch_sub",
"__tsan_atomic8_fetch_and",
"__tsan_atomic16_fetch_and",
"__tsan_atomic32_fetch_and",
"__tsan_atomic64_fetch_and",
"__tsan_atomic8_fetch_or",
"__tsan_atomic16_fetch_or",
"__tsan_atomic32_fetch_or",
"__tsan_atomic64_fetch_or",
"__tsan_atomic8_fetch_xor",
"__tsan_atomic16_fetch_xor",
"__tsan_atomic32_fetch_xor",
"__tsan_atomic64_fetch_xor",
"__tsan_atomic8_fetch_nand",
"__tsan_atomic16_fetch_nand",
"__tsan_atomic32_fetch_nand",
"__tsan_atomic64_fetch_nand",
"__tsan_atomic8_compare_exchange_strong",
"__tsan_atomic16_compare_exchange_strong",
"__tsan_atomic32_compare_exchange_strong",
"__tsan_atomic64_compare_exchange_strong",
"__tsan_atomic8_compare_exchange_weak",
"__tsan_atomic16_compare_exchange_weak",
"__tsan_atomic32_compare_exchange_weak",
"__tsan_atomic64_compare_exchange_weak",
"__tsan_atomic8_compare_exchange_val",
"__tsan_atomic16_compare_exchange_val",
"__tsan_atomic32_compare_exchange_val",
"__tsan_atomic64_compare_exchange_val",
"__tsan_atomic_thread_fence",
"__tsan_atomic_signal_fence",
/* KCOV */
"write_comp_data",
"check_kcov_mode",
"__sanitizer_cov_trace_pc",
"__sanitizer_cov_trace_const_cmp1",
"__sanitizer_cov_trace_const_cmp2",
"__sanitizer_cov_trace_const_cmp4",
"__sanitizer_cov_trace_const_cmp8",
"__sanitizer_cov_trace_cmp1",
"__sanitizer_cov_trace_cmp2",
"__sanitizer_cov_trace_cmp4",
"__sanitizer_cov_trace_cmp8",
"__sanitizer_cov_trace_switch",
/* UBSAN */
"ubsan_type_mismatch_common",
"__ubsan_handle_type_mismatch",
"__ubsan_handle_type_mismatch_v1",
"__ubsan_handle_shift_out_of_bounds",
/* misc */
"csum_partial_copy_generic",
"copy_mc_fragile",
"copy_mc_fragile_handle_tail",
"copy_mc_enhanced_fast_string",
"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
NULL
};
static void add_uaccess_safe(struct objtool_file *file)
{
struct symbol *func;
const char **name;
if (!uaccess)
return;
for (name = uaccess_safe_builtin; *name; name++) {
func = find_symbol_by_name(file->elf, *name);
if (!func)
continue;
func->uaccess_safe = true;
}
}
/*
* FIXME: For now, just ignore any alternatives which add retpolines. This is
* a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
* But it at least allows objtool to understand the control flow *around* the
* retpoline.
*/
static int add_ignore_alternatives(struct objtool_file *file)
{
struct section *sec;
struct reloc *reloc;
struct instruction *insn;
sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
if (!sec)
return 0;
list_for_each_entry(reloc, &sec->reloc_list, list) {
if (reloc->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s", sec->name);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (!insn) {
WARN("bad .discard.ignore_alts entry");
return -1;
}
insn->ignore_alts = true;
}
return 0;
}
/*
* Find the destination instructions for all jumps.
*/
static int add_jump_destinations(struct objtool_file *file)
{
struct instruction *insn;
struct reloc *reloc;
struct section *dest_sec;
unsigned long dest_off;
for_each_insn(file, insn) {
if (!is_static_jump(insn))
continue;
reloc = find_reloc_by_dest_range(file->elf, insn->sec,
insn->offset, insn->len);
if (!reloc) {
dest_sec = insn->sec;
dest_off = arch_jump_destination(insn);
} else if (reloc->sym->type == STT_SECTION) {
dest_sec = reloc->sym->sec;
dest_off = arch_dest_reloc_offset(reloc->addend);
} else if (!strncmp(reloc->sym->name, "__x86_indirect_thunk_", 21) ||
!strncmp(reloc->sym->name, "__x86_retpoline_", 16)) {
/*
* Retpoline jumps are really dynamic jumps in
* disguise, so convert them accordingly.
*/
if (insn->type == INSN_JUMP_UNCONDITIONAL)
insn->type = INSN_JUMP_DYNAMIC;
else
insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
insn->retpoline_safe = true;
continue;
} else if (insn->func) {
/* internal or external sibling call (with reloc) */
insn->call_dest = reloc->sym;
if (insn->call_dest->static_call_tramp) {
list_add_tail(&insn->static_call_node,
&file->static_call_list);
}
continue;
} else if (reloc->sym->sec->idx) {
dest_sec = reloc->sym->sec;
dest_off = reloc->sym->sym.st_value +
arch_dest_reloc_offset(reloc->addend);
} else {
/* non-func asm code jumping to another file */
continue;
}
insn->jump_dest = find_insn(file, dest_sec, dest_off);
if (!insn->jump_dest) {
/*
* This is a special case where an alt instruction
* jumps past the end of the section. These are
* handled later in handle_group_alt().
*/
if (!strcmp(insn->sec->name, ".altinstr_replacement"))
continue;
WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
insn->sec, insn->offset, dest_sec->name,
dest_off);
return -1;
}
/*
* Cross-function jump.
*/
if (insn->func && insn->jump_dest->func &&
insn->func != insn->jump_dest->func) {
/*
* For GCC 8+, create parent/child links for any cold
* subfunctions. This is _mostly_ redundant with a
* similar initialization in read_symbols().
*
* If a function has aliases, we want the *first* such
* function in the symbol table to be the subfunction's
* parent. In that case we overwrite the
* initialization done in read_symbols().
*
* However this code can't completely replace the
* read_symbols() code because this doesn't detect the
* case where the parent function's only reference to a
* subfunction is through a jump table.
*/
if (!strstr(insn->func->name, ".cold") &&
strstr(insn->jump_dest->func->name, ".cold")) {
insn->func->cfunc = insn->jump_dest->func;
insn->jump_dest->func->pfunc = insn->func;
} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
insn->jump_dest->offset == insn->jump_dest->func->offset) {
/* internal sibling call (without reloc) */
insn->call_dest = insn->jump_dest->func;
if (insn->call_dest->static_call_tramp) {
list_add_tail(&insn->static_call_node,
&file->static_call_list);
}
}
}
}
return 0;
}
static void remove_insn_ops(struct instruction *insn)
{
struct stack_op *op, *tmp;
list_for_each_entry_safe(op, tmp, &insn->stack_ops, list) {
list_del(&op->list);
free(op);
}
}
static struct symbol *find_call_destination(struct section *sec, unsigned long offset)
{
struct symbol *call_dest;
call_dest = find_func_by_offset(sec, offset);
if (!call_dest)
call_dest = find_symbol_by_offset(sec, offset);
return call_dest;
}
/*
* Find the destination instructions for all calls.
*/
static int add_call_destinations(struct objtool_file *file)
{
struct instruction *insn;
unsigned long dest_off;
struct reloc *reloc;
for_each_insn(file, insn) {
if (insn->type != INSN_CALL)
continue;
reloc = find_reloc_by_dest_range(file->elf, insn->sec,
insn->offset, insn->len);
if (!reloc) {
dest_off = arch_jump_destination(insn);
insn->call_dest = find_call_destination(insn->sec, dest_off);
if (insn->ignore)
continue;
if (!insn->call_dest) {
WARN_FUNC("unannotated intra-function call", insn->sec, insn->offset);
return -1;
}
if (insn->func && insn->call_dest->type != STT_FUNC) {
WARN_FUNC("unsupported call to non-function",
insn->sec, insn->offset);
return -1;
}
} else if (reloc->sym->type == STT_SECTION) {
dest_off = arch_dest_reloc_offset(reloc->addend);
insn->call_dest = find_call_destination(reloc->sym->sec,
dest_off);
if (!insn->call_dest) {
WARN_FUNC("can't find call dest symbol at %s+0x%lx",
insn->sec, insn->offset,
reloc->sym->sec->name,
dest_off);
return -1;
}
} else
insn->call_dest = reloc->sym;
/*
* Many compilers cannot disable KCOV with a function attribute
* so they need a little help, NOP out any KCOV calls from noinstr
* text.
*/
if (insn->sec->noinstr &&
!strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
if (reloc) {
reloc->type = R_NONE;
elf_write_reloc(file->elf, reloc);
}
elf_write_insn(file->elf, insn->sec,
insn->offset, insn->len,
arch_nop_insn(insn->len));
insn->type = INSN_NOP;
}
if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) {
if (reloc) {
reloc->type = R_NONE;
elf_write_reloc(file->elf, reloc);
}
elf_write_insn(file->elf, insn->sec,
insn->offset, insn->len,
arch_nop_insn(insn->len));
insn->type = INSN_NOP;
list_add_tail(&insn->mcount_loc_node,
&file->mcount_loc_list);
}
/*
* Whatever stack impact regular CALLs have, should be undone
* by the RETURN of the called function.
*
* Annotated intra-function calls retain the stack_ops but
* are converted to JUMP, see read_intra_function_calls().
*/
remove_insn_ops(insn);
}
return 0;
}
/*
* The .alternatives section requires some extra special care over and above
* other special sections because alternatives are patched in place.
*/
static int handle_group_alt(struct objtool_file *file,
struct special_alt *special_alt,
struct instruction *orig_insn,
struct instruction **new_insn)
{
struct instruction *last_orig_insn, *last_new_insn = NULL, *insn, *nop = NULL;
struct alt_group *orig_alt_group, *new_alt_group;
unsigned long dest_off;
orig_alt_group = malloc(sizeof(*orig_alt_group));
if (!orig_alt_group) {
WARN("malloc failed");
return -1;
}
orig_alt_group->cfi = calloc(special_alt->orig_len,
sizeof(struct cfi_state *));
if (!orig_alt_group->cfi) {
WARN("calloc failed");
return -1;
}
last_orig_insn = NULL;
insn = orig_insn;
sec_for_each_insn_from(file, insn) {
if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
break;
insn->alt_group = orig_alt_group;
last_orig_insn = insn;
}
orig_alt_group->orig_group = NULL;
orig_alt_group->first_insn = orig_insn;
orig_alt_group->last_insn = last_orig_insn;
new_alt_group = malloc(sizeof(*new_alt_group));
if (!new_alt_group) {
WARN("malloc failed");
return -1;
}
if (special_alt->new_len < special_alt->orig_len) {
/*
* Insert a fake nop at the end to make the replacement
* alt_group the same size as the original. This is needed to
* allow propagate_alt_cfi() to do its magic. When the last
* instruction affects the stack, the instruction after it (the
* nop) will propagate the new state to the shared CFI array.
*/
nop = malloc(sizeof(*nop));
if (!nop) {
WARN("malloc failed");
return -1;
}
memset(nop, 0, sizeof(*nop));
INIT_LIST_HEAD(&nop->alts);
INIT_LIST_HEAD(&nop->stack_ops);
init_cfi_state(&nop->cfi);
nop->sec = special_alt->new_sec;
nop->offset = special_alt->new_off + special_alt->new_len;
nop->len = special_alt->orig_len - special_alt->new_len;
nop->type = INSN_NOP;
nop->func = orig_insn->func;
nop->alt_group = new_alt_group;
nop->ignore = orig_insn->ignore_alts;
}
if (!special_alt->new_len) {
*new_insn = nop;
goto end;
}
insn = *new_insn;
sec_for_each_insn_from(file, insn) {
struct reloc *alt_reloc;
if (insn->offset >= special_alt->new_off + special_alt->new_len)
break;
last_new_insn = insn;
insn->ignore = orig_insn->ignore_alts;
insn->func = orig_insn->func;
insn->alt_group = new_alt_group;
/*
* Since alternative replacement code is copy/pasted by the
* kernel after applying relocations, generally such code can't
* have relative-address relocation references to outside the
* .altinstr_replacement section, unless the arch's
* alternatives code can adjust the relative offsets
* accordingly.
*/
alt_reloc = find_reloc_by_dest_range(file->elf, insn->sec,
insn->offset, insn->len);
if (alt_reloc &&
!arch_support_alt_relocation(special_alt, insn, alt_reloc)) {
WARN_FUNC("unsupported relocation in alternatives section",
insn->sec, insn->offset);
return -1;
}
if (!is_static_jump(insn))
continue;
if (!insn->immediate)
continue;
dest_off = arch_jump_destination(insn);
if (dest_off == special_alt->new_off + special_alt->new_len)
insn->jump_dest = next_insn_same_sec(file, last_orig_insn);
if (!insn->jump_dest) {
WARN_FUNC("can't find alternative jump destination",
insn->sec, insn->offset);
return -1;
}
}
if (!last_new_insn) {
WARN_FUNC("can't find last new alternative instruction",
special_alt->new_sec, special_alt->new_off);
return -1;
}
if (nop)
list_add(&nop->list, &last_new_insn->list);
end:
new_alt_group->orig_group = orig_alt_group;
new_alt_group->first_insn = *new_insn;
new_alt_group->last_insn = nop ? : last_new_insn;
new_alt_group->cfi = orig_alt_group->cfi;
return 0;
}
/*
* A jump table entry can either convert a nop to a jump or a jump to a nop.
* If the original instruction is a jump, make the alt entry an effective nop
* by just skipping the original instruction.
*/
static int handle_jump_alt(struct objtool_file *file,
struct special_alt *special_alt,
struct instruction *orig_insn,
struct instruction **new_insn)
{
if (orig_insn->type == INSN_NOP)
return 0;
if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
WARN_FUNC("unsupported instruction at jump label",
orig_insn->sec, orig_insn->offset);
return -1;
}
*new_insn = list_next_entry(orig_insn, list);
return 0;
}
/*
* Read all the special sections which have alternate instructions which can be
* patched in or redirected to at runtime. Each instruction having alternate
* instruction(s) has them added to its insn->alts list, which will be
* traversed in validate_branch().
*/
static int add_special_section_alts(struct objtool_file *file)
{
struct list_head special_alts;
struct instruction *orig_insn, *new_insn;
struct special_alt *special_alt, *tmp;
struct alternative *alt;
int ret;
ret = special_get_alts(file->elf, &special_alts);
if (ret)
return ret;
list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
orig_insn = find_insn(file, special_alt->orig_sec,
special_alt->orig_off);
if (!orig_insn) {
WARN_FUNC("special: can't find orig instruction",
special_alt->orig_sec, special_alt->orig_off);
ret = -1;
goto out;
}
new_insn = NULL;
if (!special_alt->group || special_alt->new_len) {
new_insn = find_insn(file, special_alt->new_sec,
special_alt->new_off);
if (!new_insn) {
WARN_FUNC("special: can't find new instruction",
special_alt->new_sec,
special_alt->new_off);
ret = -1;
goto out;
}
}
if (special_alt->group) {
if (!special_alt->orig_len) {
WARN_FUNC("empty alternative entry",
orig_insn->sec, orig_insn->offset);
continue;
}
ret = handle_group_alt(file, special_alt, orig_insn,
&new_insn);
if (ret)
goto out;
} else if (special_alt->jump_or_nop) {
ret = handle_jump_alt(file, special_alt, orig_insn,
&new_insn);
if (ret)
goto out;
}
alt = malloc(sizeof(*alt));
if (!alt) {
WARN("malloc failed");
ret = -1;
goto out;
}
alt->insn = new_insn;
alt->skip_orig = special_alt->skip_orig;
orig_insn->ignore_alts |= special_alt->skip_alt;
list_add_tail(&alt->list, &orig_insn->alts);
list_del(&special_alt->list);
free(special_alt);
}
out:
return ret;
}
static int add_jump_table(struct objtool_file *file, struct instruction *insn,
struct reloc *table)
{
struct reloc *reloc = table;
struct instruction *dest_insn;
struct alternative *alt;
struct symbol *pfunc = insn->func->pfunc;
unsigned int prev_offset = 0;
/*
* Each @reloc is a switch table relocation which points to the target
* instruction.
*/
list_for_each_entry_from(reloc, &table->sec->reloc_list, list) {
/* Check for the end of the table: */
if (reloc != table && reloc->jump_table_start)
break;
/* Make sure the table entries are consecutive: */
if (prev_offset && reloc->offset != prev_offset + 8)
break;
/* Detect function pointers from contiguous objects: */
if (reloc->sym->sec == pfunc->sec &&
reloc->addend == pfunc->offset)
break;
dest_insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (!dest_insn)
break;
/* Make sure the destination is in the same function: */
if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
break;
alt = malloc(sizeof(*alt));
if (!alt) {
WARN("malloc failed");
return -1;
}
alt->insn = dest_insn;
list_add_tail(&alt->list, &insn->alts);
prev_offset = reloc->offset;
}
if (!prev_offset) {
WARN_FUNC("can't find switch jump table",
insn->sec, insn->offset);
return -1;
}
return 0;
}
/*
* find_jump_table() - Given a dynamic jump, find the switch jump table
* associated with it.
*/
static struct reloc *find_jump_table(struct objtool_file *file,
struct symbol *func,
struct instruction *insn)
{
struct reloc *table_reloc;
struct instruction *dest_insn, *orig_insn = insn;
/*
* Backward search using the @first_jump_src links, these help avoid
* much of the 'in between' code. Which avoids us getting confused by
* it.
*/
for (;
insn && insn->func && insn->func->pfunc == func;
insn = insn->first_jump_src ?: prev_insn_same_sym(file, insn)) {
if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
break;
/* allow small jumps within the range */
if (insn->type == INSN_JUMP_UNCONDITIONAL &&
insn->jump_dest &&
(insn->jump_dest->offset <= insn->offset ||
insn->jump_dest->offset > orig_insn->offset))
break;
table_reloc = arch_find_switch_table(file, insn);
if (!table_reloc)
continue;
dest_insn = find_insn(file, table_reloc->sym->sec, table_reloc->addend);
if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
continue;
return table_reloc;
}
return NULL;
}
/*
* First pass: Mark the head of each jump table so that in the next pass,
* we know when a given jump table ends and the next one starts.
*/
static void mark_func_jump_tables(struct objtool_file *file,
struct symbol *func)
{
struct instruction *insn, *last = NULL;
struct reloc *reloc;
func_for_each_insn(file, func, insn) {
if (!last)
last = insn;
/*
* Store back-pointers for unconditional forward jumps such
* that find_jump_table() can back-track using those and
* avoid some potentially confusing code.
*/
if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
insn->offset > last->offset &&
insn->jump_dest->offset > insn->offset &&
!insn->jump_dest->first_jump_src) {
insn->jump_dest->first_jump_src = insn;
last = insn->jump_dest;
}
if (insn->type != INSN_JUMP_DYNAMIC)
continue;
reloc = find_jump_table(file, func, insn);
if (reloc) {
reloc->jump_table_start = true;
insn->jump_table = reloc;
}
}
}
static int add_func_jump_tables(struct objtool_file *file,
struct symbol *func)
{
struct instruction *insn;
int ret;
func_for_each_insn(file, func, insn) {
if (!insn->jump_table)
continue;
ret = add_jump_table(file, insn, insn->jump_table);
if (ret)
return ret;
}
return 0;
}
/*
* For some switch statements, gcc generates a jump table in the .rodata
* section which contains a list of addresses within the function to jump to.
* This finds these jump tables and adds them to the insn->alts lists.
*/
static int add_jump_table_alts(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;
int ret;
if (!file->rodata)
return 0;
for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
mark_func_jump_tables(file, func);
ret = add_func_jump_tables(file, func);
if (ret)
return ret;
}
}
return 0;
}
static void set_func_state(struct cfi_state *state)
{
state->cfa = initial_func_cfi.cfa;
memcpy(&state->regs, &initial_func_cfi.regs,
CFI_NUM_REGS * sizeof(struct cfi_reg));
state->stack_size = initial_func_cfi.cfa.offset;
}
static int read_unwind_hints(struct objtool_file *file)
{
struct section *sec, *relocsec;
struct reloc *reloc;
struct unwind_hint *hint;
struct instruction *insn;
int i;
sec = find_section_by_name(file->elf, ".discard.unwind_hints");
if (!sec)
return 0;
relocsec = sec->reloc;
if (!relocsec) {
WARN("missing .rela.discard.unwind_hints section");
return -1;
}
if (sec->len % sizeof(struct unwind_hint)) {
WARN("struct unwind_hint size mismatch");
return -1;
}
file->hints = true;
for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
hint = (struct unwind_hint *)sec->data->d_buf + i;
reloc = find_reloc_by_dest(file->elf, sec, i * sizeof(*hint));
if (!reloc) {
WARN("can't find reloc for unwind_hints[%d]", i);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (!insn) {
WARN("can't find insn for unwind_hints[%d]", i);
return -1;
}
insn->hint = true;
if (hint->type == UNWIND_HINT_TYPE_FUNC) {
set_func_state(&insn->cfi);
continue;
}
if (arch_decode_hint_reg(insn, hint->sp_reg)) {
WARN_FUNC("unsupported unwind_hint sp base reg %d",
insn->sec, insn->offset, hint->sp_reg);
return -1;
}
insn->cfi.cfa.offset = bswap_if_needed(hint->sp_offset);
insn->cfi.type = hint->type;
insn->cfi.end = hint->end;
}
return 0;
}
static int read_retpoline_hints(struct objtool_file *file)
{
struct section *sec;
struct instruction *insn;
struct reloc *reloc;
sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
if (!sec)
return 0;
list_for_each_entry(reloc, &sec->reloc_list, list) {
if (reloc->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s", sec->name);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (!insn) {
WARN("bad .discard.retpoline_safe entry");
return -1;
}
if (insn->type != INSN_JUMP_DYNAMIC &&
insn->type != INSN_CALL_DYNAMIC) {
WARN_FUNC("retpoline_safe hint not an indirect jump/call",
insn->sec, insn->offset);
return -1;
}
insn->retpoline_safe = true;
}
return 0;
}
static int read_instr_hints(struct objtool_file *file)
{
struct section *sec;
struct instruction *insn;
struct reloc *reloc;
sec = find_section_by_name(file->elf, ".rela.discard.instr_end");
if (!sec)
return 0;
list_for_each_entry(reloc, &sec->reloc_list, list) {
if (reloc->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s", sec->name);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (!insn) {
WARN("bad .discard.instr_end entry");
return -1;
}
insn->instr--;
}
sec = find_section_by_name(file->elf, ".rela.discard.instr_begin");
if (!sec)
return 0;
list_for_each_entry(reloc, &sec->reloc_list, list) {
if (reloc->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s", sec->name);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (!insn) {
WARN("bad .discard.instr_begin entry");
return -1;
}
insn->instr++;
}
return 0;
}
static int read_intra_function_calls(struct objtool_file *file)
{
struct instruction *insn;
struct section *sec;
struct reloc *reloc;
sec = find_section_by_name(file->elf, ".rela.discard.intra_function_calls");
if (!sec)
return 0;
list_for_each_entry(reloc, &sec->reloc_list, list) {
unsigned long dest_off;
if (reloc->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s",
sec->name);
return -1;
}
insn = find_insn(file, reloc->sym->sec, reloc->addend);
if (!insn) {
WARN("bad .discard.intra_function_call entry");
return -1;
}
if (insn->type != INSN_CALL) {
WARN_FUNC("intra_function_call not a direct call",
insn->sec, insn->offset);
return -1;
}
/*
* Treat intra-function CALLs as JMPs, but with a stack_op.
* See add_call_destinations(), which strips stack_ops from
* normal CALLs.
*/
insn->type = INSN_JUMP_UNCONDITIONAL;
dest_off = insn->offset + insn->len + insn->immediate;
insn->jump_dest = find_insn(file, insn->sec, dest_off);
if (!insn->jump_dest) {
WARN_FUNC("can't find call dest at %s+0x%lx",
insn->sec, insn->offset,
insn->sec->name, dest_off);
return -1;
}
}
return 0;
}
static int read_static_call_tramps(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;
for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->bind == STB_GLOBAL &&
!strncmp(func->name, STATIC_CALL_TRAMP_PREFIX_STR,
strlen(STATIC_CALL_TRAMP_PREFIX_STR)))
func->static_call_tramp = true;
}
}
return 0;
}
static void mark_rodata(struct objtool_file *file)
{
struct section *sec;
bool found = false;
/*
* Search for the following rodata sections, each of which can
* potentially contain jump tables:
*
* - .rodata: can contain GCC switch tables
* - .rodata.<func>: same, if -fdata-sections is being used
* - .rodata..c_jump_table: contains C annotated jump tables
*
* .rodata.str1.* sections are ignored; they don't contain jump tables.
*/
for_each_sec(file, sec) {
if (!strncmp(sec->name, ".rodata", 7) &&
!strstr(sec->name, ".str1.")) {
sec->rodata = true;
found = true;
}
}
file->rodata = found;
}
static int decode_sections(struct objtool_file *file)
{
int ret;
mark_rodata(file);
ret = decode_instructions(file);
if (ret)
return ret;
ret = add_dead_ends(file);
if (ret)
return ret;
add_ignores(file);
add_uaccess_safe(file);
ret = add_ignore_alternatives(file);
if (ret)
return ret;
ret = read_static_call_tramps(file);
if (ret)
return ret;
ret = add_jump_destinations(file);
if (ret)
return ret;
ret = add_special_section_alts(file);
if (ret)
return ret;
ret = read_intra_function_calls(file);
if (ret)
return ret;
ret = add_call_destinations(file);
if (ret)
return ret;
ret = add_jump_table_alts(file);
if (ret)
return ret;
ret = read_unwind_hints(file);
if (ret)
return ret;
ret = read_retpoline_hints(file);
if (ret)
return ret;
ret = read_instr_hints(file);
if (ret)
return ret;
return 0;
}
static bool is_fentry_call(struct instruction *insn)
{
if (insn->type == INSN_CALL && insn->call_dest &&
insn->call_dest->type == STT_NOTYPE &&
!strcmp(insn->call_dest->name, "__fentry__"))
return true;
return false;
}
static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
{
struct cfi_state *cfi = &state->cfi;
int i;
if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
return true;
if (cfi->cfa.offset != initial_func_cfi.cfa.offset)
return true;
if (cfi->stack_size != initial_func_cfi.cfa.offset)
return true;
for (i = 0; i < CFI_NUM_REGS; i++) {
if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
return true;
}
return false;
}
static bool check_reg_frame_pos(const struct cfi_reg *reg,
int expected_offset)
{
return reg->base == CFI_CFA &&
reg->offset == expected_offset;
}
static bool has_valid_stack_frame(struct insn_state *state)
{
struct cfi_state *cfi = &state->cfi;
if (cfi->cfa.base == CFI_BP &&
check_reg_frame_pos(&cfi->regs[CFI_BP], -cfi->cfa.offset) &&
check_reg_frame_pos(&cfi->regs[CFI_RA], -cfi->cfa.offset + 8))
return true;
if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
return true;
return false;
}
static int update_cfi_state_regs(struct instruction *insn,
struct cfi_state *cfi,
struct stack_op *op)
{
struct cfi_reg *cfa = &cfi->cfa;
if (cfa->base != CFI_SP && cfa->base != CFI_SP_INDIRECT)
return 0;
/* push */
if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
cfa->offset += 8;
/* pop */
if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
cfa->offset -= 8;
/* add immediate to sp */
if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
cfa->offset -= op->src.offset;
return 0;
}
static void save_reg(struct cfi_state *cfi, unsigned char reg, int base, int offset)
{
if (arch_callee_saved_reg(reg) &&
cfi->regs[reg].base == CFI_UNDEFINED) {
cfi->regs[reg].base = base;
cfi->regs[reg].offset = offset;
}
}
static void restore_reg(struct cfi_state *cfi, unsigned char reg)
{
cfi->regs[reg].base = initial_func_cfi.regs[reg].base;
cfi->regs[reg].offset = initial_func_cfi.regs[reg].offset;
}
/*
* A note about DRAP stack alignment:
*
* GCC has the concept of a DRAP register, which is used to help keep track of
* the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
* register. The typical DRAP pattern is:
*
* 4c 8d 54 24 08 lea 0x8(%rsp),%r10
* 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
* 41 ff 72 f8 pushq -0x8(%r10)
* 55 push %rbp
* 48 89 e5 mov %rsp,%rbp
* (more pushes)
* 41 52 push %r10
* ...
* 41 5a pop %r10
* (more pops)
* 5d pop %rbp
* 49 8d 62 f8 lea -0x8(%r10),%rsp
* c3 retq
*
* There are some variations in the epilogues, like:
*
* 5b pop %rbx
* 41 5a pop %r10
* 41 5c pop %r12
* 41 5d pop %r13
* 41 5e pop %r14
* c9 leaveq
* 49 8d 62 f8 lea -0x8(%r10),%rsp
* c3 retq
*
* and:
*
* 4c 8b 55 e8 mov -0x18(%rbp),%r10
* 48 8b 5d e0 mov -0x20(%rbp),%rbx
* 4c 8b 65 f0 mov -0x10(%rbp),%r12
* 4c 8b 6d f8 mov -0x8(%rbp),%r13
* c9 leaveq
* 49 8d 62 f8 lea -0x8(%r10),%rsp
* c3 retq
*
* Sometimes r13 is used as the DRAP register, in which case it's saved and
* restored beforehand:
*
* 41 55 push %r13
* 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
* 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
* ...
* 49 8d 65 f0 lea -0x10(%r13),%rsp
* 41 5d pop %r13
* c3 retq
*/
static int update_cfi_state(struct instruction *insn,
struct instruction *next_insn,
struct cfi_state *cfi, struct stack_op *op)
{
struct cfi_reg *cfa = &cfi->cfa;
struct cfi_reg *regs = cfi->regs;
/* stack operations don't make sense with an undefined CFA */
if (cfa->base == CFI_UNDEFINED) {
if (insn->func) {
WARN_FUNC("undefined stack state", insn->sec, insn->offset);
return -1;
}
return 0;
}
if (cfi->type == UNWIND_HINT_TYPE_REGS ||
cfi->type == UNWIND_HINT_TYPE_REGS_PARTIAL)
return update_cfi_state_regs(insn, cfi, op);
switch (op->dest.type) {
case OP_DEST_REG:
switch (op->src.type) {
case OP_SRC_REG:
if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
cfa->base == CFI_SP &&
check_reg_frame_pos(&regs[CFI_BP], -cfa->offset)) {
/* mov %rsp, %rbp */
cfa->base = op->dest.reg;
cfi->bp_scratch = false;
}
else if (op->src.reg == CFI_SP &&
op->dest.reg == CFI_BP && cfi->drap) {
/* drap: mov %rsp, %rbp */
regs[CFI_BP].base = CFI_BP;
regs[CFI_BP].offset = -cfi->stack_size;
cfi->bp_scratch = false;
}
else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
/*
* mov %rsp, %reg
*
* This is needed for the rare case where GCC
* does:
*
* mov %rsp, %rax
* ...
* mov %rax, %rsp
*/
cfi->vals[op->dest.reg].base = CFI_CFA;
cfi->vals[op->dest.reg].offset = -cfi->stack_size;
}
else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
(cfa->base == CFI_BP || cfa->base == cfi->drap_reg)) {
/*
* mov %rbp, %rsp
*
* Restore the original stack pointer (Clang).
*/
cfi->stack_size = -cfi->regs[CFI_BP].offset;
}
else if (op->dest.reg == cfa->base) {
/* mov %reg, %rsp */
if (cfa->base == CFI_SP &&
cfi->vals[op->src.reg].base == CFI_CFA) {
/*
* This is needed for the rare case
* where GCC does something dumb like:
*
* lea 0x8(%rsp), %rcx
* ...
* mov %rcx, %rsp
*/
cfa->offset = -cfi->vals[op->src.reg].offset;
cfi->stack_size = cfa->offset;
} else if (cfa->base == CFI_SP &&
cfi->vals[op->src.reg].base == CFI_SP_INDIRECT &&
cfi->vals[op->src.reg].offset == cfa->offset) {
/*
* Stack swizzle:
*
* 1: mov %rsp, (%[tos])
* 2: mov %[tos], %rsp
* ...
* 3: pop %rsp
*
* Where:
*
* 1 - places a pointer to the previous
* stack at the Top-of-Stack of the
* new stack.
*
* 2 - switches to the new stack.
*
* 3 - pops the Top-of-Stack to restore
* the original stack.
*
* Note: we set base to SP_INDIRECT
* here and preserve offset. Therefore
* when the unwinder reaches ToS it
* will dereference SP and then add the
* offset to find the next frame, IOW:
* (%rsp) + offset.
*/
cfa->base = CFI_SP_INDIRECT;
} else {
cfa->base = CFI_UNDEFINED;
cfa->offset = 0;
}
}
else if (op->dest.reg == CFI_SP &&
cfi->vals[op->src.reg].base == CFI_SP_INDIRECT &&
cfi->vals[op->src.reg].offset == cfa->offset) {
/*
* The same stack swizzle case 2) as above. But
* because we can't change cfa->base, case 3)
* will become a regular POP. Pretend we're a
* PUSH so things don't go unbalanced.
*/
cfi->stack_size += 8;
}
break;
case OP_SRC_ADD:
if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
/* add imm, %rsp */
cfi->stack_size -= op->src.offset;
if (cfa->base == CFI_SP)
cfa->offset -= op->src.offset;
break;
}
if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
/* lea disp(%rbp), %rsp */
cfi->stack_size = -(op->src.offset + regs[CFI_BP].offset);
break;
}
if (!cfi->drap && op->src.reg == CFI_SP &&
op->dest.reg == CFI_BP && cfa->base == CFI_SP &&
check_reg_frame_pos(&regs[CFI_BP], -cfa->offset + op->src.offset)) {
/* lea disp(%rsp), %rbp */
cfa->base = CFI_BP;
cfa->offset -= op->src.offset;
cfi->bp_scratch = false;
break;
}
if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
/* drap: lea disp(%rsp), %drap */
cfi->drap_reg = op->dest.reg;
/*
* lea disp(%rsp), %reg
*
* This is needed for the rare case where GCC
* does something dumb like:
*
* lea 0x8(%rsp), %rcx
* ...
* mov %rcx, %rsp
*/
cfi->vals[op->dest.reg].base = CFI_CFA;
cfi->vals[op->dest.reg].offset = \
-cfi->stack_size + op->src.offset;
break;
}
if (cfi->drap && op->dest.reg == CFI_SP &&
op->src.reg == cfi->drap_reg) {
/* drap: lea disp(%drap), %rsp */
cfa->base = CFI_SP;
cfa->offset = cfi->stack_size = -op->src.offset;
cfi->drap_reg = CFI_UNDEFINED;
cfi->drap = false;
break;
}
if (op->dest.reg == cfi->cfa.base && !(next_insn && next_insn->hint)) {
WARN_FUNC("unsupported stack register modification",
insn->sec, insn->offset);
return -1;
}
break;
case OP_SRC_AND:
if (op->dest.reg != CFI_SP ||
(cfi->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
(cfi->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
WARN_FUNC("unsupported stack pointer realignment",
insn->sec, insn->offset);
return -1;
}
if (cfi->drap_reg != CFI_UNDEFINED) {
/* drap: and imm, %rsp */
cfa->base = cfi->drap_reg;
cfa->offset = cfi->stack_size = 0;
cfi->drap = true;
}
/*
* Older versions of GCC (4.8ish) realign the stack
* without DRAP, with a frame pointer.
*/
break;
case OP_SRC_POP:
case OP_SRC_POPF:
if (op->dest.reg == CFI_SP && cfa->base == CFI_SP_INDIRECT) {
/* pop %rsp; # restore from a stack swizzle */
cfa->base = CFI_SP;
break;
}
if (!cfi->drap && op->dest.reg == cfa->base) {
/* pop %rbp */
cfa->base = CFI_SP;
}
if (cfi->drap && cfa->base == CFI_BP_INDIRECT &&
op->dest.reg == cfi->drap_reg &&
cfi->drap_offset == -cfi->stack_size) {
/* drap: pop %drap */
cfa->base = cfi->drap_reg;
cfa->offset = 0;
cfi->drap_offset = -1;
} else if (cfi->stack_size == -regs[op->dest.reg].offset) {
/* pop %reg */
restore_reg(cfi, op->dest.reg);
}
cfi->stack_size -= 8;
if (cfa->base == CFI_SP)
cfa->offset -= 8;
break;
case OP_SRC_REG_INDIRECT:
if (!cfi->drap && op->dest.reg == cfa->base &&
op->dest.reg == CFI_BP) {
/* mov disp(%rsp), %rbp */
cfa->base = CFI_SP;
cfa->offset = cfi->stack_size;
}
if (cfi->drap && op->src.reg == CFI_BP &&
op->src.offset == cfi->drap_offset) {
/* drap: mov disp(%rbp), %drap */
cfa->base = cfi->drap_reg;
cfa->offset = 0;
cfi->drap_offset = -1;
}
if (cfi->drap && op->src.reg == CFI_BP &&
op->src.offset == regs[op->dest.reg].offset) {
/* drap: mov disp(%rbp), %reg */
restore_reg(cfi, op->dest.reg);
} else if (op->src.reg == cfa->base &&
op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
/* mov disp(%rbp), %reg */
/* mov disp(%rsp), %reg */
restore_reg(cfi, op->dest.reg);
} else if (op->src.reg == CFI_SP &&
op->src.offset == regs[op->dest.reg].offset + cfi->stack_size) {
/* mov disp(%rsp), %reg */
restore_reg(cfi, op->dest.reg);
}
break;
default:
WARN_FUNC("unknown stack-related instruction",
insn->sec, insn->offset);
return -1;
}
break;
case OP_DEST_PUSH:
case OP_DEST_PUSHF:
cfi->stack_size += 8;
if (cfa->base == CFI_SP)
cfa->offset += 8;
if (op->src.type != OP_SRC_REG)
break;
if (cfi->drap) {
if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
/* drap: push %drap */
cfa->base = CFI_BP_INDIRECT;
cfa->offset = -cfi->stack_size;
/* save drap so we know when to restore it */
cfi->drap_offset = -cfi->stack_size;
} else if (op->src.reg == CFI_BP && cfa->base == cfi->drap_reg) {
/* drap: push %rbp */
cfi->stack_size = 0;
} else {
/* drap: push %reg */
save_reg(cfi, op->src.reg, CFI_BP, -cfi->stack_size);
}
} else {
/* push %reg */
save_reg(cfi, op->src.reg, CFI_CFA, -cfi->stack_size);
}
/* detect when asm code uses rbp as a scratch register */
if (!no_fp && insn->func && op->src.reg == CFI_BP &&
cfa->base != CFI_BP)
cfi->bp_scratch = true;
break;
case OP_DEST_REG_INDIRECT:
if (cfi->drap) {
if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
/* drap: mov %drap, disp(%rbp) */
cfa->base = CFI_BP_INDIRECT;
cfa->offset = op->dest.offset;
/* save drap offset so we know when to restore it */
cfi->drap_offset = op->dest.offset;
} else {
/* drap: mov reg, disp(%rbp) */
save_reg(cfi, op->src.reg, CFI_BP, op->dest.offset);
}
} else if (op->dest.reg == cfa->base) {
/* mov reg, disp(%rbp) */
/* mov reg, disp(%rsp) */
save_reg(cfi, op->src.reg, CFI_CFA,
op->dest.offset - cfi->cfa.offset);
} else if (op->dest.reg == CFI_SP) {
/* mov reg, disp(%rsp) */
save_reg(cfi, op->src.reg, CFI_CFA,
op->dest.offset - cfi->stack_size);
} else if (op->src.reg == CFI_SP && op->dest.offset == 0) {
/* mov %rsp, (%reg); # setup a stack swizzle. */
cfi->vals[op->dest.reg].base = CFI_SP_INDIRECT;
cfi->vals[op->dest.reg].offset = cfa->offset;
}
break;
case OP_DEST_MEM:
if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
WARN_FUNC("unknown stack-related memory operation",
insn->sec, insn->offset);
return -1;
}
/* pop mem */
cfi->stack_size -= 8;
if (cfa->base == CFI_SP)
cfa->offset -= 8;
break;
default:
WARN_FUNC("unknown stack-related instruction",
insn->sec, insn->offset);
return -1;
}
return 0;
}
/*
* The stack layouts of alternatives instructions can sometimes diverge when
* they have stack modifications. That's fine as long as the potential stack
* layouts don't conflict at any given potential instruction boundary.
*
* Flatten the CFIs of the different alternative code streams (both original
* and replacement) into a single shared CFI array which can be used to detect
* conflicts and nicely feed a linear array of ORC entries to the unwinder.
*/
static int propagate_alt_cfi(struct objtool_file *file, struct instruction *insn)
{
struct cfi_state **alt_cfi;
int group_off;
if (!insn->alt_group)
return 0;
alt_cfi = insn->alt_group->cfi;
group_off = insn->offset - insn->alt_group->first_insn->offset;
if (!alt_cfi[group_off]) {
alt_cfi[group_off] = &insn->cfi;
} else {
if (memcmp(alt_cfi[group_off], &insn->cfi, sizeof(struct cfi_state))) {
WARN_FUNC("stack layout conflict in alternatives",
insn->sec, insn->offset);
return -1;
}
}
return 0;
}
static int handle_insn_ops(struct instruction *insn,
struct instruction *next_insn,
struct insn_state *state)
{
struct stack_op *op;
list_for_each_entry(op, &insn->stack_ops, list) {
if (update_cfi_state(insn, next_insn, &state->cfi, op))
return 1;
if (op->dest.type == OP_DEST_PUSHF) {
if (!state->uaccess_stack) {
state->uaccess_stack = 1;
} else if (state->uaccess_stack >> 31) {
WARN_FUNC("PUSHF stack exhausted",
insn->sec, insn->offset);
return 1;
}
state->uaccess_stack <<= 1;
state->uaccess_stack |= state->uaccess;
}
if (op->src.type == OP_SRC_POPF) {
if (state->uaccess_stack) {
state->uaccess = state->uaccess_stack & 1;
state->uaccess_stack >>= 1;
if (state->uaccess_stack == 1)
state->uaccess_stack = 0;
}
}
}
return 0;
}
static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
{
struct cfi_state *cfi1 = &insn->cfi;
int i;
if (memcmp(&cfi1->cfa, &cfi2->cfa, sizeof(cfi1->cfa))) {
WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
insn->sec, insn->offset,
cfi1->cfa.base, cfi1->cfa.offset,
cfi2->cfa.base, cfi2->cfa.offset);
} else if (memcmp(&cfi1->regs, &cfi2->regs, sizeof(cfi1->regs))) {
for (i = 0; i < CFI_NUM_REGS; i++) {
if (!memcmp(&cfi1->regs[i], &cfi2->regs[i],
sizeof(struct cfi_reg)))
continue;
WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
insn->sec, insn->offset,
i, cfi1->regs[i].base, cfi1->regs[i].offset,
i, cfi2->regs[i].base, cfi2->regs[i].offset);
break;
}
} else if (cfi1->type != cfi2->type) {
WARN_FUNC("stack state mismatch: type1=%d type2=%d",
insn->sec, insn->offset, cfi1->type, cfi2->type);
} else if (cfi1->drap != cfi2->drap ||
(cfi1->drap && cfi1->drap_reg != cfi2->drap_reg) ||
(cfi1->drap && cfi1->drap_offset != cfi2->drap_offset)) {
WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
insn->sec, insn->offset,
cfi1->drap, cfi1->drap_reg, cfi1->drap_offset,
cfi2->drap, cfi2->drap_reg, cfi2->drap_offset);
} else
return true;
return false;
}
static inline bool func_uaccess_safe(struct symbol *func)
{
if (func)
return func->uaccess_safe;
return false;
}
static inline const char *call_dest_name(struct instruction *insn)
{
if (insn->call_dest)
return insn->call_dest->name;
return "{dynamic}";
}
static inline bool noinstr_call_dest(struct symbol *func)
{
/*
* We can't deal with indirect function calls at present;
* assume they're instrumented.
*/
if (!func)
return false;
/*
* If the symbol is from a noinstr section; we good.
*/
if (func->sec->noinstr)
return true;
/*
* The __ubsan_handle_*() calls are like WARN(), they only happen when
* something 'BAD' happened. At the risk of taking the machine down,
* let them proceed to get the message out.
*/
if (!strncmp(func->name, "__ubsan_handle_", 15))
return true;
return false;
}
static int validate_call(struct instruction *insn, struct insn_state *state)
{
if (state->noinstr && state->instr <= 0 &&
!noinstr_call_dest(insn->call_dest)) {
WARN_FUNC("call to %s() leaves .noinstr.text section",
insn->sec, insn->offset, call_dest_name(insn));
return 1;
}
if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
WARN_FUNC("call to %s() with UACCESS enabled",
insn->sec, insn->offset, call_dest_name(insn));
return 1;
}
if (state->df) {
WARN_FUNC("call to %s() with DF set",
insn->sec, insn->offset, call_dest_name(insn));
return 1;
}
return 0;
}
static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
{
if (has_modified_stack_frame(insn, state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
insn->sec, insn->offset);
return 1;
}
return validate_call(insn, state);
}
static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
{
if (state->noinstr && state->instr > 0) {
WARN_FUNC("return with instrumentation enabled",
insn->sec, insn->offset);
return 1;
}
if (state->uaccess && !func_uaccess_safe(func)) {
WARN_FUNC("return with UACCESS enabled",
insn->sec, insn->offset);
return 1;
}
if (!state->uaccess && func_uaccess_safe(func)) {
WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
insn->sec, insn->offset);
return 1;
}
if (state->df) {
WARN_FUNC("return with DF set",
insn->sec, insn->offset);
return 1;
}
if (func && has_modified_stack_frame(insn, state)) {
WARN_FUNC("return with modified stack frame",
insn->sec, insn->offset);
return 1;
}
if (state->cfi.bp_scratch) {
WARN_FUNC("BP used as a scratch register",
insn->sec, insn->offset);
return 1;
}
return 0;
}
static struct instruction *next_insn_to_validate(struct objtool_file *file,
struct instruction *insn)
{
struct alt_group *alt_group = insn->alt_group;
/*
* Simulate the fact that alternatives are patched in-place. When the
* end of a replacement alt_group is reached, redirect objtool flow to
* the end of the original alt_group.
*/
if (alt_group && insn == alt_group->last_insn && alt_group->orig_group)
return next_insn_same_sec(file, alt_group->orig_group->last_insn);
return next_insn_same_sec(file, insn);
}
/*
* Follow the branch starting at the given instruction, and recursively follow
* any other branches (jumps). Meanwhile, track the frame pointer state at
* each instruction and validate all the rules described in
* tools/objtool/Documentation/stack-validation.txt.
*/
static int validate_branch(struct objtool_file *file, struct symbol *func,
struct instruction *insn, struct insn_state state)
{
struct alternative *alt;
struct instruction *next_insn;
struct section *sec;
u8 visited;
int ret;
sec = insn->sec;
while (1) {
next_insn = next_insn_to_validate(file, insn);
if (file->c_file && func && insn->func && func != insn->func->pfunc) {
WARN("%s() falls through to next function %s()",
func->name, insn->func->name);
return 1;
}
if (func && insn->ignore) {
WARN_FUNC("BUG: why am I validating an ignored function?",
sec, insn->offset);
return 1;
}
visited = 1 << state.uaccess;
if (insn->visited) {
if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
return 1;
if (insn->visited & visited)
return 0;
}
if (state.noinstr)
state.instr += insn->instr;
if (insn->hint)
state.cfi = insn->cfi;
else
insn->cfi = state.cfi;
insn->visited |= visited;
if (propagate_alt_cfi(file, insn))
return 1;
if (!insn->ignore_alts && !list_empty(&insn->alts)) {
bool skip_orig = false;
list_for_each_entry(alt, &insn->alts, list) {
if (alt->skip_orig)
skip_orig = true;
ret = validate_branch(file, func, alt->insn, state);
if (ret) {
if (backtrace)
BT_FUNC("(alt)", insn);
return ret;
}
}
if (skip_orig)
return 0;
}
if (handle_insn_ops(insn, next_insn, &state))
return 1;
switch (insn->type) {
case INSN_RETURN:
return validate_return(func, insn, &state);
case INSN_CALL:
case INSN_CALL_DYNAMIC:
ret = validate_call(insn, &state);
if (ret)
return ret;
if (!no_fp && func && !is_fentry_call(insn) &&
!has_valid_stack_frame(&state)) {
WARN_FUNC("call without frame pointer save/setup",
sec, insn->offset);
return 1;
}
if (dead_end_function(file, insn->call_dest))
return 0;
if (insn->type == INSN_CALL && insn->call_dest->static_call_tramp) {
list_add_tail(&insn->static_call_node,
&file->static_call_list);
}
break;
case INSN_JUMP_CONDITIONAL:
case INSN_JUMP_UNCONDITIONAL:
if (is_sibling_call(insn)) {
ret = validate_sibling_call(insn, &state);
if (ret)
return ret;
} else if (insn->jump_dest) {
ret = validate_branch(file, func,
insn->jump_dest, state);
if (ret) {
if (backtrace)
BT_FUNC("(branch)", insn);
return ret;
}
}
if (insn->type == INSN_JUMP_UNCONDITIONAL)
return 0;
break;
case INSN_JUMP_DYNAMIC:
case INSN_JUMP_DYNAMIC_CONDITIONAL:
if (is_sibling_call(insn)) {
ret = validate_sibling_call(insn, &state);
if (ret)
return ret;
}
if (insn->type == INSN_JUMP_DYNAMIC)
return 0;
break;
case INSN_CONTEXT_SWITCH:
if (func && (!next_insn || !next_insn->hint)) {
WARN_FUNC("unsupported instruction in callable function",
sec, insn->offset);
return 1;
}
return 0;
case INSN_STAC:
if (state.uaccess) {
WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
return 1;
}
state.uaccess = true;
break;
case INSN_CLAC:
if (!state.uaccess && func) {
WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
return 1;
}
if (func_uaccess_safe(func) && !state.uaccess_stack) {
WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
return 1;
}
state.uaccess = false;
break;
case INSN_STD:
if (state.df) {
WARN_FUNC("recursive STD", sec, insn->offset);
return 1;
}
state.df = true;
break;
case INSN_CLD:
if (!state.df && func) {
WARN_FUNC("redundant CLD", sec, insn->offset);
return 1;
}
state.df = false;
break;
default:
break;
}
if (insn->dead_end)
return 0;
if (!next_insn) {
if (state.cfi.cfa.base == CFI_UNDEFINED)
return 0;
WARN("%s: unexpected end of section", sec->name);
return 1;
}
insn = next_insn;
}
return 0;
}
static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
{
struct instruction *insn;
struct insn_state state;
int ret, warnings = 0;
if (!file->hints)
return 0;
init_insn_state(&state, sec);
if (sec) {
insn = find_insn(file, sec, 0);
if (!insn)
return 0;
} else {
insn = list_first_entry(&file->insn_list, typeof(*insn), list);
}
while (&insn->list != &file->insn_list && (!sec || insn->sec == sec)) {
if (insn->hint && !insn->visited) {
ret = validate_branch(file, insn->func, insn, state);
if (ret && backtrace)
BT_FUNC("<=== (hint)", insn);
warnings += ret;
}
insn = list_next_entry(insn, list);
}
return warnings;
}
static int validate_retpoline(struct objtool_file *file)
{
struct instruction *insn;
int warnings = 0;
for_each_insn(file, insn) {
if (insn->type != INSN_JUMP_DYNAMIC &&
insn->type != INSN_CALL_DYNAMIC)
continue;
if (insn->retpoline_safe)
continue;
/*
* .init.text code is ran before userspace and thus doesn't
* strictly need retpolines, except for modules which are
* loaded late, they very much do need retpoline in their
* .init.text
*/
if (!strcmp(insn->sec->name, ".init.text") && !module)
continue;
WARN_FUNC("indirect %s found in RETPOLINE build",
insn->sec, insn->offset,
insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
warnings++;
}
return warnings;
}
static bool is_kasan_insn(struct instruction *insn)
{
return (insn->type == INSN_CALL &&
!strcmp(insn->call_dest->name, "__asan_handle_no_return"));
}
static bool is_ubsan_insn(struct instruction *insn)
{
return (insn->type == INSN_CALL &&
!strcmp(insn->call_dest->name,
"__ubsan_handle_builtin_unreachable"));
}
static bool ignore_unreachable_insn(struct objtool_file *file, struct instruction *insn)
{
int i;
struct instruction *prev_insn;
if (insn->ignore || insn->type == INSN_NOP)
return true;
/*
* Ignore any unused exceptions. This can happen when a whitelisted
* function has an exception table entry.
*
* Also ignore alternative replacement instructions. This can happen
* when a whitelisted function uses one of the ALTERNATIVE macros.
*/
if (!strcmp(insn->sec->name, ".fixup") ||
!strcmp(insn->sec->name, ".altinstr_replacement") ||
!strcmp(insn->sec->name, ".altinstr_aux"))
return true;
if (!insn->func)
return false;
/*
* CONFIG_UBSAN_TRAP inserts a UD2 when it sees
* __builtin_unreachable(). The BUG() macro has an unreachable() after
* the UD2, which causes GCC's undefined trap logic to emit another UD2
* (or occasionally a JMP to UD2).
*
* It may also insert a UD2 after calling a __noreturn function.
*/
prev_insn = list_prev_entry(insn, list);
if ((prev_insn->dead_end || dead_end_function(file, prev_insn->call_dest)) &&
(insn->type == INSN_BUG ||
(insn->type == INSN_JUMP_UNCONDITIONAL &&
insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
return true;
/*
* Check if this (or a subsequent) instruction is related to
* CONFIG_UBSAN or CONFIG_KASAN.
*
* End the search at 5 instructions to avoid going into the weeds.
*/
for (i = 0; i < 5; i++) {
if (is_kasan_insn(insn) || is_ubsan_insn(insn))
return true;
if (insn->type == INSN_JUMP_UNCONDITIONAL) {
if (insn->jump_dest &&
insn->jump_dest->func == insn->func) {
insn = insn->jump_dest;
continue;
}
break;
}
if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
break;
insn = list_next_entry(insn, list);
}
return false;
}
static int validate_symbol(struct objtool_file *file, struct section *sec,
struct symbol *sym, struct insn_state *state)
{
struct instruction *insn;
int ret;
if (!sym->len) {
WARN("%s() is missing an ELF size annotation", sym->name);
return 1;
}
if (sym->pfunc != sym || sym->alias != sym)
return 0;
insn = find_insn(file, sec, sym->offset);
if (!insn || insn->ignore || insn->visited)
return 0;
state->uaccess = sym->uaccess_safe;
ret = validate_branch(file, insn->func, insn, *state);
if (ret && backtrace)
BT_FUNC("<=== (sym)", insn);
return ret;
}
static int validate_section(struct objtool_file *file, struct section *sec)
{
struct insn_state state;
struct symbol *func;
int warnings = 0;
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
init_insn_state(&state, sec);
set_func_state(&state.cfi);
warnings += validate_symbol(file, sec, func, &state);
}
return warnings;
}
static int validate_vmlinux_functions(struct objtool_file *file)
{
struct section *sec;
int warnings = 0;
sec = find_section_by_name(file->elf, ".noinstr.text");
if (sec) {
warnings += validate_section(file, sec);
warnings += validate_unwind_hints(file, sec);
}
sec = find_section_by_name(file->elf, ".entry.text");
if (sec) {
warnings += validate_section(file, sec);
warnings += validate_unwind_hints(file, sec);
}
return warnings;
}
static int validate_functions(struct objtool_file *file)
{
struct section *sec;
int warnings = 0;
for_each_sec(file, sec) {
if (!(sec->sh.sh_flags & SHF_EXECINSTR))
continue;
warnings += validate_section(file, sec);
}
return warnings;
}
static int validate_reachable_instructions(struct objtool_file *file)
{
struct instruction *insn;
if (file->ignore_unreachables)
return 0;
for_each_insn(file, insn) {
if (insn->visited || ignore_unreachable_insn(file, insn))
continue;
WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
return 1;
}
return 0;
}
int check(struct objtool_file *file)
{
int ret, warnings = 0;
arch_initial_func_cfi_state(&initial_func_cfi);
ret = decode_sections(file);
if (ret < 0)
goto out;
warnings += ret;
if (list_empty(&file->insn_list))
goto out;
if (vmlinux && !validate_dup) {
ret = validate_vmlinux_functions(file);
if (ret < 0)
goto out;
warnings += ret;
goto out;
}
if (retpoline) {
ret = validate_retpoline(file);
if (ret < 0)
return ret;
warnings += ret;
}
ret = validate_functions(file);
if (ret < 0)
goto out;
warnings += ret;
ret = validate_unwind_hints(file, NULL);
if (ret < 0)
goto out;
warnings += ret;
if (!warnings) {
ret = validate_reachable_instructions(file);
if (ret < 0)
goto out;
warnings += ret;
}
ret = create_static_call_sections(file);
if (ret < 0)
goto out;
warnings += ret;
if (mcount) {
ret = create_mcount_loc_sections(file);
if (ret < 0)
goto out;
warnings += ret;
}
out:
/*
* For now, don't fail the kernel build on fatal warnings. These
* errors are still fairly common due to the growing matrix of
* supported toolchains and their recent pace of change.
*/
return 0;
}
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